[BUG] Dart incorrect nullable when required

Bug Report Checklist

• [ X] Have you provided a full/minimal spec to reproduce the issue?
• [ X] Have you validated the input using an OpenAPI validator?
• [ X] Have you tested with the latest master to confirm the issue still exists?
• [ X] Have you searched for related issues/PRs?
• [ X] What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Right now nullable but required properties are marked as not nullable despite being clearly set to nullable. #21508 references the inverse issue of this with includeIfNull.

If the field is marked as nullable, then the property generated in dart should be nullable. There is no case where a field marked as nullable shouldn't, yet it is flagging repeatCycle as not nullable in dart while it clearly knows thati t was set to nullable.

openapi-generator version

7.12.0

OpenAPI declaration file content or url

"TodoDto": {
        "type": "object",
        "description": "Todo",
        "additionalProperties": false,
        "required": [
          "id",
          "createdOn",
          "createdBy",
          "callLogId",
          "subject",
          "description",
          "contacts",
          "categories",
          "reminderDateTime",
          "repeatCycle",
          "remindLocation",
          "status",
          "priority"
        ],
        "properties": {
          "id": {
            "type": "string",
            "format": "uuid",
            "nullable": true
          },
          "createdOn": {
            "type": "string",
            "description": "Created On",
            "format": "date-time",
            "nullable": false
          },
          "createdBy": {
            "description": "Created By",
            "nullable": false,
            "$ref": "#/components/schemas/ContactRefDto"
          },
          "callLogId": {
            "type": "string",
            "description": "Call Log Referenced",
            "format": "uuid",
            "nullable": true
          },
          "subject": {
            "type": "string",
            "description": "Subject",
            "nullable": false
          },
          "description": {
            "type": "string",
            "description": "Description",
            "nullable": true
          },
          "contacts": {
            "type": "array",
            "description": "Contacts",
            "nullable": false,
            "items": {
              "$ref": "#/components/schemas/ContactRefDto"
            }
          },
          "categories": {
            "type": "array",
            "description": "Categories",
            "nullable": false,
            "items": {
              "$ref": "#/components/schemas/CategoryRefDto"
            }
          },
          "reminderDateTime": {
            "type": "string",
            "description": "Remind On",
            "format": "date-time",
            "nullable": true
          },
          "repeatCycle": {
            "description": "Repeat Cycle",
            "nullable": true,
            "$ref": "#/components/schemas/RepeatCycles"
          },
          "remindLocation": {
            "description": "Remind Location",
            "nullable": true,
            "$ref": "#/components/schemas/Location"
          },
          "status": {
            "description": "Status",
            "nullable": false,
            "$ref": "#/components/schemas/TodoStatuses"
          },
          "priority": {
            "description": "Priority",
            "nullable": false,
            "$ref": "#/components/schemas/Priorities"
          }
        }
      },

Results in:

@JsonSerializable(
  checked: true,
  createToJson: true,
  disallowUnrecognizedKeys: false,
  explicitToJson: true,
)
class TodoDto {
  /// Returns a new [TodoDto] instance.
  TodoDto({
    required this.id,
    required this.createdOn,
    required this.createdBy,
    required this.callLogId,
    required this.subject,
    required this.description,
    required this.contacts,
    required this.categories,
    required this.reminderDateTime,
    required this.repeatCycle,
    required this.remindLocation,
    required this.status,
    required this.priority,
  });

  @JsonKey(
    name: r'id',
    required: true,
    includeIfNull: true,
  )
  final String? id;

  /// Created On
  @JsonKey(
    name: r'createdOn',
    required: true,
    includeIfNull: true,
  )
  final DateTime createdOn;

  @JsonKey(
    name: r'createdBy',
    required: true,
    includeIfNull: true,
  )
  final ContactRefDto createdBy;

  /// Call Log Referenced
  @JsonKey(
    name: r'callLogId',
    required: true,
    includeIfNull: true,
  )
  final String? callLogId;

  /// Subject
  @JsonKey(
    name: r'subject',
    required: true,
    includeIfNull: true,
  )
  final String subject;

  /// Description
  @JsonKey(
    name: r'description',
    required: true,
    includeIfNull: true,
  )
  final String? description;

  /// Contacts
  @JsonKey(
    name: r'contacts',
    required: true,
    includeIfNull: true,
  )
  final List<ContactRefDto> contacts;

  /// Categories
  @JsonKey(
    name: r'categories',
    required: true,
    includeIfNull: true,
  )
  final List<CategoryRefDto> categories;

  /// Remind On
  @JsonKey(
    name: r'reminderDateTime',
    required: true,
    includeIfNull: true,
  )
  final DateTime? reminderDateTime;

  @JsonKey(
    name: r'repeatCycle',
    required: true,
    includeIfNull: true,
  )
  final RepeatCycles repeatCycle;

  @JsonKey(
    name: r'remindLocation',
    required: true,
    includeIfNull: true,
  )
  final Location remindLocation;

  @JsonKey(
    name: r'status',
    required: true,
    includeIfNull: true,
  )
  final TodoStatuses status;

  @JsonKey(
    name: r'priority',
    required: true,
    includeIfNull: true,
  )
  final Priorities priority;

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is TodoDto &&
          other.id == id &&
          other.createdOn == createdOn &&
          other.createdBy == createdBy &&
          other.callLogId == callLogId &&
          other.subject == subject &&
          other.description == description &&
          other.contacts == contacts &&
          other.categories == categories &&
          other.reminderDateTime == reminderDateTime &&
          other.repeatCycle == repeatCycle &&
          other.remindLocation == remindLocation &&
          other.status == status &&
          other.priority == priority;

  @override
  int get hashCode =>
      (id == null ? 0 : id.hashCode) +
      createdOn.hashCode +
      createdBy.hashCode +
      (callLogId == null ? 0 : callLogId.hashCode) +
      subject.hashCode +
      (description == null ? 0 : description.hashCode) +
      contacts.hashCode +
      categories.hashCode +
      (reminderDateTime == null ? 0 : reminderDateTime.hashCode) +
      repeatCycle.hashCode +
      remindLocation.hashCode +
      status.hashCode +
      priority.hashCode;

  factory TodoDto.fromJson(Map<String, dynamic> json) =>
      _$TodoDtoFromJson(json);

  Map<String, dynamic> toJson() => _$TodoDtoToJson(this);

  @override
  String toString() {
    return toJson().toString();
  }
}

Generation Details

				"@openapitools/openapi-generator-cli",
				"generate",
				"-i",
				"http://localhost:16049/help/v1/openapi.json",
				"-g",
				"dart-dio",
				"-c",
				"open-generator-config.yaml",
				"--enable-post-process-file"

Steps to reproduce

Generate with the above command against the snippet provided.

Related issues/PRs

#21508

Suggest a fix

If the field is defined as "nullable": true, then the property generated 100% of the time should be nullable. Per #21508, the required array defines if it should be sent even if null, not the status as nullable. If OpenAPI had a default value then that is what it would be set to if not required and not nullable.

Reproduce the issue with the provided OpenAPI schema using the dart-dio generator and open-generator-config.yaml; begin by tracing how required and nullable properties are handled. Done means fields marked nullable: true, including required fields such as repeatCycle, are generated with nullable Dart types while remaining required for serialization.